The invention resides in a photocell (solar cell). In a photocell or, respectively, solar cell, a charge carrier pair is generated by light. The charge carriers are conducted away separately. In this way, an electric current is produced.
So called Gratzel cells are known (B. O'Regan, M. Gratzel, Nature 353 (1991), 737), wherein a coloring substance layer is deposited on porous titanium oxide, which acts as an electrode. The coloring substance layer is in contact with a counter electrode by way of an electrolyte solution. The titanium oxide serves as carrier for the coloring substance and as semi-conductor electrode by way of which electrons transferred by light radiation from the coloring substance to the titanium oxide are carried away. The electric circuit is closed by way of the counter electrode and the electrolyte solution and the coloring substance, which is oxidized during the electron transfer, is again reduced.
Instead of by an electrolyte solution, the coloring substance can be contacted also by way of conductive polymers. However, then the efficiency is lower. It is only 3% as compared to 10.5% with wet-chemical cells.
It is disadvantageous that the coloring substance layer is unevenly distributed on the porous titanium dioxide. In areas where the layer is too thin, the light is not sufficiently absorbed. In areas where the layer is too thick, the absorbed light cannot be fully utilized for the generation of charge carrier pairs. Also, in many applications, the contacting of the coloring substance by a liquid electrolyte is disadvantageous.
In addition to the Gratzel solar cells, other solar cells are known, which include so-called interpenetrating networks of organic compounds (N. S. Sacriciftci, A. J. Heeger, Synthetic Metals 70 (1995), 1349). Such a network represents a kind of mixed phase of two contact materials in the solar cell.
It is further known to make, in a solar cell of the type referred to above, a first material particularly rough (J. Desilvestro, M. Gratzel, L. Kavon, J. Moser, J. Am. Chem. Soc. 107 (1985), 2988). A sufficient roughness is obtained for an organic semi-conductor by a suitable deposition procedure. The desired roughness can also be obtained by etching of organic semiconductors.
In the mixed phase, there is a phase A and a phase B. Phase A and phase B form either a photo-voltaic active transition (where a photo voltage and a photo current are generated by exposure to light) or a so-called injection contact. An injection contact is a contact between an excitable molecule or an excitable material and a semi-conductor. Upon excitation of a molecule, or respectively, the material, a charge carrier of a charge carrier pair generated by light excitation moves from the molecule or, respectively, material to the semi-conductor. In the case of injection, another phase C interfaces with the phase B. The phase C is such that the other charge carrier of the charge carrier pair is carried away.
A phase C adjoining the phase B can also be provided in the case of the classic photovoltaic active transition. The phase C then assumes the same function as in the case of the injection. With a direct photovoltaic transition, it is however not necessary to provide a phase C.
In a solar cell, there is an ohmic transition between the phase A and an electrode (a so-called front contact). The same is true for the phase B, or respectively, the phase C with respect to a counter electrode.
It is the object of the present invention to provide a method for the manufacture of a solar cell, which is improved over those known in the art and to provide a solar cell made by the method according to the invention.